Tech WondersPlay

Mind-Bending Math & GamesUnsolved Problems

The Simplest Unsolved Problem

Halve if even, triple and add one if odd; does it always reach 1?

A rule so simple a child can follow it has beaten every mathematician for almost a century. Want to try the numbers yourself?

You'll find out

  • The two rules that fit in one breath
  • A small number with a wild ride
  • Why checking is not proving

Why it matters

It shows the gap between testing and proving, the one that matters every time software is called “bug-free”.

About 3 min6 interactive slides · 5 questionsLesson 128 · Zone 15

Play this lesson

Free to play in your browser or on iPhone

More in this zone

  1. 127Auditory PerceptionYanny or Laurel?One recording, two words, and people hear different ones
  2. 129Internet HistoryThe First YouTube VideoNineteen seconds at a zoo started it all
  3. 130BiomimicryThe Train That Copied a BirdJapan's bullet train borrowed its nose from a kingfisher
  4. 131StatisticsWhat ‘70% Chance of Rain’ MeansIt isn't 70% of the day or 70% of the city
  5. 132PerceptionYour Brain Hides Your NoseYour nose is always in view, yet you never see it
  6. 133Precision MeasurementThe Atomic ClockThe most precise clocks count the vibrations inside atoms
  7. 134Satellite NavigationHow GPS Finds YouYour phone listens to satellites' clocks and does the math
  8. 135Mathematics in NatureSunflowers Count in FibonacciSeed spirals come in 34s, 55s and 89s